The first one. The use of irrigation.
Many people decided to move from more rural areas that offered land and space for farming to cities that had factories and offered job opportunities
This website could help you http://www.weather.gov/cle/Seasons
The math suggests that for every parsec the rate of moving away is 71 km/s, so when two galaxies are separated by two parsecs we come to 142 km/s speed of moving away from each other. If we take the first light ever (from what is known so far) the cosmic microwave radiation, is 46 billion light-years away from us at all directions, which comes at 4,200 megaparsecs, which comes at 13.7 billion light-years, so it will come to 29,820,000 km/s. It all depends from the distance between the galaxies which is calculated by their type of colour and movement in comparison to other galaxies.